1. Field of the Invention
The present invention relates to a method and arrangement for the processing of quantities, such as current, voltage, power or moment, measured or calculated by a power converter apparatus consisting of power converter units, e.g. for generating a summed or average quantity. For the sake of simplicity, in the following description of the invention only current is considered, but the same method and system can as well be applied to the processing of other quantities, too.
The invention relates e.g. to an arrangement where a high-power frequency converter apparatus consists of a plurality of parallel-connected lower-power frequency converter or inverter units. In such an arrangement, the component current of each frequency converter is measured, and these currents are then summed e.g. to regulate the load, such as an alternating-current motor, connected to the frequency converter apparatus.
2. Discussion of the Background
For parallel connection of frequency converter units controlling an alternating-current motor, it is necessary that the component load currents measured by the power units be summed in order that the motor regulating function active in the control unit should get correct information regarding the motor current. When a prior-art solution is used, this results in a delay problem in data transfer, because the data regarding the component currents are first received in a summing unit, added together and only the summed current data is transmitted to the control unit. In parallel connection, data transfer is thus slowed down at least by the delay caused by the summing and retransmission, which at the same time also results in slower motor regulation.